how can I create a procedural circuit board texture
It would be VERY DIFFICULT do do this procedurally in blender using cycles nodes. This could be done in Substance Designer without as much sweat, but that still might prove a challenge.

A free, easy tool to achieve this affect is JSplacment.
This lightweight program excels at generating unique and customizable sci-fi patterns for use in CG programs, like blender.

To get started with JSplacment, you can download it here: https://windmillart.net/?p=jsplacement

A good tutorial for these patterns is this: https://youtu.be/ee59XU3fKFw
(He uses C4D as his main 3D program, but the way you create them for use in Blender is identical)

I hope this helps!